An angioplasty catheter is typically elongate and tubular, and is provided with a balloon near or at its distal end and radiopaque bands defining the extremities of the balloon. The catheter is inserted at a convenient location and fed into the stenosed blood vessel until the balloon is located in the narrowed portion of the blood vessel. Fluid from an external supply is then used to inflate the balloon such that it compresses the obstructing plaque and stretches the plaque coated walls of the blood vessel. When the physician is satisfied that the blood vessel has been widened sufficiently, the balloon is deflated and the catheter removed.
Angioplasty catheters have been successfully used for a number of years in the treatment of blood vessels obstructed or stenosed with plaque. An angioplasty catheter includes, near its distal end, a balloon which can be inflated by means of pressurized fluid supplied through a lumen in the catheter. The treatment involves the location of the balloon in the stenosed section of the blood vessel, followed by inflation and deflation. During inflation, the balloon compresses the plaque and stretches the blood vessel such that the cross-sectional area of the stenosis is increased until it is comparable to that of the unobstructed blood vessel. When the treatment has been completed the balloon is deflated and the catheter removed. The treated blood vessel maintains substantially its enlarged cross-section to permit the free flow of blood through this portion.
To perform satisfactorily a suitable angioplasty catheter must possess a number of properties. For ease of insertion it is preferable that the catheter is flexible, has a relatively small cross-sectional area, and has a smooth outer surface. Also, the method of insertion of the catheter has a significant bearing on the form of the catheter. The catheter which is the subject of the present invention is intended for insertion using the Seldinger technique and therefore preferably has a tapered end and a lumen to receive the Seldinger guide wire. The catheter ends at an aperture in the tapered end substantially coaxially with the main body of the catheter. However, perhaps the most important part of the catheter is the balloon which must be strong enough to withstand the application of high pressures without rupture and which must always inflate to a predetermined shape and size.
Also, during insertion and removal, the balloon must present a small profile as it is moved longitudinally.
It has long been accepted that in order to reduce the balloon profile during insertion, the balloon must be wrapped in some way about the body. An example of a typical structure intended for this purpose is found in U.S. Pat. No. 4,338,942 to Fogarty. The balloon is attached to an internal rod which has an exposed control knob at the proximal end of the catheter. On turning the knob, the balloon is rotated at the distal end to impart a twist which wraps the balloon on the main body. There is no energy stored other than possibly in the balloon. After insertion, the twist is removed to allow inflation and then, to permit removal, the twist is again applied. This structure is rather complex and requires a long rod through the length of the device. Further, this structure is not suitable for insertion using the Seldinger technique.
Another exemplary structure which uses a mechanical wrapping device is shown in U.S. Pat. No. 4,646,719 to Neuman et al. A tube runs the length of the device to permit Seldinger insertion through the tube and this tube can be rotated to wrap the balloon against the resistance of a spring. After insertion, the spring energy can return the balloon to its normal position for inflation. During insertion the balloon must be kept in the wrapped condition against the urging of the spring which will tend to unwrap the balloon.
A different approach is taught in U.S. Pat. No. 4,402,307 to Hanson et al. A balloon is provided which is attached at its distal end to a tubular central member which extends along the length of the catheter. A tool is provided for engaging the distal end to rotate that end and wrap the balloon around the tube as energy is stored in the twisted tube. Provided that sufficient vacuum is applied, the balloon will remain in this condition during insertion. Should there be any difficulty with the vacuum then of course the balloon will unwrap itself under the influence of the tube returning to its normal condition. After insertion, the balloon is released and can not be wrapped again in the same fashion in which it was wrapped in the first place. However access is provided to the tube at the proximal end for rotating the tube which will presumably wrap the balloon in the fashion taught by Fogarty.
All of the prior art structures suffer from serious disadvantages and among them are complexity, dangerous situations arising should vacuum fail during insertion, and such difficulties as unwrapping the balloon accurately to ensure that it is in the proper position for inflation after it is located in the patient.
It is an object of the present invention to provide an improved angioplasty catheter which overcomes some of the disadvantages of the prior art.